Apparatus and method for analyzing information relating to physical and mental condition

ABSTRACT

An apparatus and method are provided for analyzing information relating to the physiological and psychological conditions of a driver. Psychological conditions such as comfortableness or degree of alertness are estimated on the basis of physical data such as fluctuation in brain waves. This apparatus comprises a first neural network having a pre-processed 1/f fluctuation signal for brain waves as an input and for estimating a degree of alertness of the driver, and a second neural network receiving the estimated degree of alertness and the pre-processed 1/f fluctuation signal, for estimating and outputting driving comfortableness. By employing a neural network, which has a mapping ability as well as flexible adaptability even for non-linear data, based on the learning function, more accurate estimation of mental conditions can be achieved in comparison with conventional statistical analysis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to an apparatus and method foranalyzing information concerning the physical and mental condition of aperson, and more particularly to an apparatus and method for relatingphysical data (physiological factors) such as brain waves with mentaldata (psychological factors) such as alertness (wakefulness) orcomfortableness (pleasantness).

2. Description of the Prior Art

People nowadays have many diversified views concerning their residence,work environment, and vehicles. The basis of selecting such things isbeing shifted from "on function" to "on human characteristics". Asimportance is thus increasingly attached to human sensitivity, a growingnumber of studies has recently begun to focus on sensitivity, orcomfortableness.

Comfortableness stems from human feeling closely related to livingconditions. The fact that feeling is subjective makes it difficult tomeasure by objective methods. Thus most evaluations for comfortablenesshave been qualitative and based on sensation, and there is virtually noestablished method of measuring it quantitatively.

As a quantitative analysis of human information, many studies forassociating physical data such as brain waves, electrodiagrams, orheartbeat data with mental data such as alertness or comfortablenesshave been conducted. These attempts intend to more accurately estimatemental (psychological) data such as alertness and comfortablenessquantitatively on the basis of physical data. Techniques of findingcorrelation between physiological factors and psychological factorsgenerally utilize statistical analysis including multiple regressionanalysis and analysis of variance so as to develop an algorithm forestimating psychological data based on the analysis results. However, nouseful algorithm has been developed yet which is sufficiently accurateand universal for practical use.

SUMMARY OF THE INVENTION

Physical and mental information inherently contain non-linear and vaguecharacteristics. Accordingly, statistic analysis, which is basically alinear method, using such data inevitably involves problems. Sinceprobabilities based on quantitative measurement of feeling are requiredfor the design of products or space offering comfortableness, objectivemeasurement and evaluation of feeling has been strongly sought after.

In view of these demands, the inventors have developed a study ofmeasurement using EEG fluctuation (i.e. 1/f fluctuation in brain waves)as an indicator and estimation through the use of a neural network(hereinafter NN). Focusing on a neural network's non-linear mappingability and adaptability based on learning functions, the inventorsutilized a neural network to develop an efficient algorithm forestimating mental data from physical data, and have established atechnique of quantitatively measuring such mental data (e.g. degree ofcomfortableness). Thus, the object of the invention is to provide anapparatus and method for estimating mental (or psychological) data basedon physical (or physiological) data such as brain waves.

In order to achieve the object, an apparatus for analyzing informationrelating to physical and mental conditions in accordance with theinvention comprises a neural network receiving a physiologicalfluctuation signal as an input and for estimating mental (orpsychological) conditions based on the physiological fluctuation signal.It is known that a physiological fluctuation signal has a close relationwith the psychological conditions of a human being, and good estimationof psychological conditions is achieved by using such a physiologicalfluctuation signal.

The physiological fluctuation signal may be an EEG fluctuation which hasbeen pre-processed. It is known that brain waves are closely associatedwith psychological conditions of a human being, and the psychologicalcondition can be satisfactorily estimated from the pre-processed EEGfluctuation signal.

The psychological conditions include degree of alertness. Alertness is abasic element of psychological conditions, and measurement of alertnessleads to good estimation of psychological conditions of a human being.

The psychological conditions further include comfortableness.Measurement of comfortableness also leads to preferable quantitativeestimation of psychological conditions.

The neural network comprises a first neural network having apre-processed EEG fluctuation signal as an input, for estimatingalertness, and a second neural network having the pre-processed EEGfluctuation signal and alertness estimated by the first neural networkas inputs, for estimating comfortableness. In this example, degree ofalertness and comfortableness are obtained for estimating psychologicalconditions. Especially, degree of alertness estimated by the firstneural network is input to the second neural network to further estimatecomfortableness. It is known that comfortableness strongly depends onthe degree of alertness, and thus, comfortableness can be estimated moreaccurately by inputting the alertness as a parameter into the secondnetwork in the above-mentioned structure.

In another aspect of the invention, there is provided a method foranalyzing physical and mental information. This method comprises thesteps of inputting a physiological fluctuation signal to a neuralnetwork, and estimating psychological conditions based on thephysiological fluctuation signal.

The physiological fluctuation signal includes an EEG fluctuation signal.

The psychological conditions include degree of alertness andcomfortableness.

This method further comprises the steps of applying the EEG fluctuationsignal to a first neural network to estimate alertness, and inputtingboth the EEG fluctuation signal and the value of alertness obtained bythe first neural network to a second neural network to further estimatecomfortableness. In this case, both alertness and comfortableness areused for estimation of psychological conditions.

In the above-mentioned aspects of the invention, psychologicalevaluations based on questionnaire surveys are supplied as teachersignals to the neural network. However, it is more preferable to trainthe neural network, rather than using questionnaire results as mainparameters, because psychological evaluation obtained by questionnairegenerally contains differences among individuals. For this reason, anhourglass type of neural network is used, in which EEG fluctuationsignals are supplied both as input and output for training the neuralnetwork. Internal expressions corresponding to psychological conditionsare obtained in the intermediate layers of the hourglass type neuralnetwork through the learning of the network.

In one example of the invention, the neural network is an hourglass typeof neural network having intermediate layers between input and outputfor learning. Both the input and output of the network are EEGfluctuation signals. Outputs of the intermediate layers represent apsychological condition. The training of the network using only EEGfluctuation signals, without relaying on questionnaire-based evaluation,achieves more accurate estimation of psychological conditions.

In the case of combining first and second neural networks for estimatingalertness and comfortableness, respectively, both neural networks arehourglass type neural networks. Output values of the intermediate layersof each neural network represent psychological conditions.

Use of hourglass type neural networks can apply to the method foranalyzing physical and mental information.

Although, EEG fluctuation signals are used as physical data for thepurpose of estimating psychological conditions, it is applicable to theestimation of working achievement, because alertness has a closerelation with the working result.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the structure of a human brain.

FIG. 2 shows the structure of an experimentation system in accordancewith the invention.

FIG. 3 is a table showing experimental data.

FIG. 4 shows an NN template configuration having a composite output ofalertness and comfortableness.

FIG. 5A shows an NN template configuration for estimating degree ofalertness based on brain wave fluctuations.

FIG. 5B shows an NN template configuration for estimatingcomfortableness based on brain wave fluctuations and alertness.

FIG. 6A shows an NN template configuration for estimatingcomfortableness based on brain wave fluctuations.

FIG. 6B shows an NN template configuration for estimating alertness pluscomfortableness based on brain wave fluctuation.

FIG. 7A is a graph showing a relationship between training data and NNestimated values based on experimental data of the alertness-estimatingneural network, where the number of neurons in the intermediate layer is35.

FIG. 7B is a graph showing a relationship between test data and NNestimated values based on experimentation data of thealertness-estimating neural network, where the number of neurons in theintermediate layer is 35.

FIG. 8A is a graph showing a relationship between training data and NNestimated values based on experimental data of the alertness-estimatingneural network, where the number of neurons in the intermediate layer is70.

FIG. 8B is a graph showing a relationship between test data and NNestimated values based on experimental data of the alertness-estimatingneural network, where the number of neurons in the intermediate layer is70.

FIG. 9A is a graph showing a relationship between training data and NNestimated values based on preliminary experiment data of thecomfortableness-estimating neural network.

FIG. 9B is a graph showing a relationship between test data and NNestimated values based on preliminary experimentation data of thecomfortableness-estimating neural network.

FIG. 10 shows a correlation between the experimental data.

FIG. 11 shows experimental conditions and results for the alertnessestimating NN.

FIG. 12 shows experimental conditions and results for thecomfortableness estimating NN.

FIG. 13 shows a structure of an hourglass type of neural network.

FIG. 14 shows graphs plotting weight of objects vs. activity of neuronsobtained as an internal expression in the intermediate layer of thehourglass type of neural network of FIG. 13.

FIG. 15 shows a detailed structure of the hourglass type of neuralnetwork.

FIGS. 16A and 16B show graphs plotting the relationship between outputvalues of the first and second unit in the third layer of the hourglasstype of neural network shown in FIG. 15, and alertness andcomfortableness obtained by questionnaire survey, respectively.

FIG. 17 illustrates a principle of obtaining degree of alertness andcomfortableness of the driver based on actual work results.

DESCRIPTION OF PREFERRED EMBODIMENT

The principle of the invention will now be described referring to theactual results of estimation of psychological conditions from EEGfluctuation.

A. MEASURING METHOD OF ALERTNESS AND COMFORTABLENESS USING FREQUENCYFLUCTUATION OF α-WAVE AS AN INDICATOR

One example of quantitative measurement of feeling is measurement usingfluctuation characteristics in α-wave as a parameter.

Brain waves detected through the scalp are represented as a voltagechange of around 50 μV having a frequency component of around 60 Hz. Inexperimentation for adults, a frequency component of 8-13 Hz isdominantly observed while resting with their eyes closed or duringrelaxation. This frequency component is called α-waves. Waves of around10 Hz appear most frequently, but do not always appear at a constantcycle, as is seen from that fact the average range is 8-13 Hz. Thefrequency speed is increased or decreased as time elapses.

A-1. 1/f Fluctuation and Comfortableness

When representing a fluctuation spectrum on the double logarithmic scalewith the vertical axis for fluctuation (power value) and the horizontalaxis for the fluctuation frequency, the power value decreases in reverseproportion to frequency f with a gradient -1 as the frequency increases.The fluctuation having this characteristic is defined as a 1/ffluctuation. Returning the fluctuation characteristics thus obtained tothe time axis gives the auto-correlation function of the fluctuation.The 1/f fluctuation, originally discovered as a physical fluctuationsuch as heat noise, does not have the same characteristics as whitenoise fluctuation which has no correlation with the past fluctuationinformation, but does keep a certain degree of correlation with the pastfluctuation as seen in the Markov linkage.

1/f fluctuation has been incorporated into recent home electricalappliances and automobile air-conditioners, where it is implicitlyassumed that anything with 1/f fluctuation occurring as time elapseswill produce a feeling of tranquility. Such an assumption is consideredto have originated in research which has revealed that, as a result ofspectrum analysis, breeze flows, rivulet sounds, and classical musicrhythms have 1/f fluctuation and that electrical stimulus with 1/ffluctuation is effective in removing pain. Many problems remain to bestudied, however, such as the relationship between stimuli with 1/ffluctuation and biorhythm and psychological conditions includingfeeling.

A-2. Logical Background of Analysis of Fluctuation Phenomenon

Generally, an autocorrelation function and a power spectrum densityfunction are used for analysis of statistical characteristics of thefluctuation phenomenon. Assuming that an irregular variable for time "t"is x(t) and a variable for time "t+τ" (τ time period later than time t)is x(t+τ), the autocorrelation function is defined by a time averagevalue of multiplication of these two variables. This is represented bythe following expression. ##EQU1##

The above formula (1) is a function of only τ, regardless of time t. Itis known that, for the formula (1), when the fluctuation is completelyrandom, the following expression is effected.

    C(τ)=0(τ≠0) C(τ)=C(0)(τ=0)           (2)

The noise having the autocorrelation value zero, when lag τ=0 is definedas white noise. The autocorrelation function is an even function whichhas the maximum value when τ=0. This is expressed by the followingexpression.

    C(0)>±C(τ)(τ≠0)                           (3)

Most fluctuations maintain the previous characteristics even after microlag time Δt to some extent. This is because of the fact that, for suchfluctuations, the value at a time "t" strongly correlates with a valueat time very close to "t" and the correlation becomes lower with a valueat a time apart from "t". The correlation decreases exponentially as thevalue τ increases, and finally becomes C(τ)=0. In other words, such afluctuation has characteristics expressed as C(τ)→0 (τ→∞). Assuming thatthe lag τ satisfying the equation C(τ)=0 is τ₀, C(τ) is expressed asfollows. ##EQU2##

In this case, the larger the lag τ₀, the slower the rate of decrease ofC(τ), which is depicted as a shape widening toward the bottom.

On the other hand, power spectrum P(f) is associated with theautocorrelation function, as expressed below, in accordance withWiener-Khintchine's formula. ##EQU3##

When incorporating the equation (5) into the equation (6), the followingequation can be obtained. ##EQU4##

In the equation (7), if frequency f corresponding to the lag τ is muchsmaller than 1/2πτ₀ (that is, 1/2πτ₀ >>f, which means 1>>2πfτ₀), thevalue (2πfτ₀)² can be almost ignored and P(f) has a constant value f₀regardless of frequency. On the other hand, if "f" is much larger than1/2πτ₀ (that is, 1/2πτ₀ <<f, which means 1<<2πfτ₀), the value of P(f)shown in the equation (5) varies depending on the value (2πfτ₀)².

Therefore, in the frequency band of 1/2πτ₀ <<f, P(f) varies inaccordance with f⁻² and the power spectrum rapidly decreases asfrequency increases. The fact that P(f) varies with a negative gradientwith respect to frequency f means that the influence of x(t) remainsuntil time τ₀. In the case that P(f) is in proportion to f⁻¹ (i.e. 1/f),the smaller the negative gradient, the higher the degree of randomness.In other words, when the negative gradient is sharp, the power spectrumexhibits a slow variation. A 1/f fluctuation is located in the middle ofthese two, which indicates that P(f) is approximately in proportion tof⁻¹.

B. EVALUATION METHOD FOR PHYSIOLOGICAL AND PSYCHOLOGICAL MEASUREMENT OFCOMFORTABLENESS

B-1. Significance of EEG Fluctuation as a Physiological Indicator ofComfortableness

Physiological responses, which are readily and noninvasively observedand have been conventionally used, include (i) central responses such asspontaneous brain waves, sensory evoked potential, or event-relatedpotential, (ii) peripheral response such as heart beat, pulse rate,breathing rate, or body temperature, and (iii) motor responses such aseye movement, blinking, or myogenic potential. Central responses havesuch disadvantages that they need laborious measurement and analysis,while peripheral responses have a disadvantage that they are subject toceiling effects for maintaining the function of a living body in spiteof simple measurement. It is therefore preferable to conductmulti-faceted measurement including peripheral responses, but centeringon brain activities (such as brain waves and brain electromagneticwaves).

The human brain consists of the two cerebral hemispheres, brain stem,and cerebellum (see FIG. 1). The cerebral hemispheres have the centercontrolling higher order mental functions, the cerebellum controls motorand balance functions, and the brain stem controls life supportfunctions. Information related to feeling is processed in thehypothalamus in the brain stem upper portion, and in the limbic systemincluding the brain called the limbic cortex existing deep in thecerebral hemispheres. The information processing of higher-order feelinginvolves the neocortex of the cerebral frontal lobe to a considerableextent. Control of alertness that affects the intensity of feelinginvolves the hypothalamus and a system called a reticular activatingsystem existing in the brain stem.

Activities relating to brain waves have a close relation with thesesystems. A recent report indicates that fluctuation of brain wavesvaries with changes in feeling or degree of alertness.

Feelings are always changing, and the time-course measurement of brainwave fluctuation is considered to be more suitable for examiningemotional changes compared with the static approach to informationprocessing as represented by evaluation of mean values in conventionalpractice.

This invention uses α-wave fluctuation in brain waves as an indicator.The α-wave frequency rhythm was observed under olfactory stimuli such asfragrance and odor, under audiovisual stimuli such as video image andsound, and under audio stimuli including natural and artificial soundsand low-frequency noise, and at the same time, psychological conditionswere recorded and classified according to characteristics. Fluctuationsin the α-wave frequency rhythm recorded were stored corresponding toclassification. FIG. 2 shows the system configuration used for theexperiment.

As a result of finding correspondence between α-wave fluctuation andsubjective alertness or comfortableness, it was discovered that thecharacteristics of α-wave fluctuation change responded to changes inpsychological conditions. The spectrum analysis of the characteristicsof assorted fluctuations in the α-wave frequency indicates that thefrequency fluctuation of α-waves exhibits a gentle rhythm(characteristic close to 1/f) during comfortable rest or a relaxingcondition, whereas such characteristics collapse in uncomfortableconditions.

It is also possible to estimate alertness and comfortableness directlyfrom EEG fluctuation characteristics without classifying psychologicalconditions. This method includes multiple regression analysis (or linearanalysis) with fluctuation characteristics as the independent variableand the psychological response as the dependent variable. Alternatively,it may include preparation of an estimation algorithm using a neuralnetwork (for non-linear analysis). It was found that, by using theseapproaches, comfortableness was estimated from EEG fluctuationcharacteristics obtained from the frontal and central regions of thebrain, and alertness was estimated from EEG fluctuation of the parietaland occipital regions of the brain with relatively high probability,details of which will be described below.

B-2. Detection and Analysis of the α-wave Frequency Fluctuation

Frequency fluctuation is measured using a system shown in FIG. 2.

(1) Measurement of Brain Waves

Brain waves comprise various complex frequency components in response tothe conditions of the living body, and are continuously fluctuating. Itis difficult to grasp the characteristics of brain waves by visualobservation. One conventional technique for examining brain waves is touse a band pass filter to extract only a specific frequency component,which is then analyzed using a computer. In this invention, detectionand analysis of fluctuation in brain waves is carried out using aexperimental system shown in FIG. 2.

(2) Detection of Fluctuation Characteristics

(i) Extraction of α-wave component

Brain waves are detected through 8 electrodes (F3, F4, C3, C4, P3, P4,01, 02) put on the head of human subject, as seen from FIG. 2. Thedetected brain waves are transmitted by an EEG transmitter 10, andreceived at an EEG telemeter 12 which has a time constant of 0.3 secondand has a high cut filter for cutting signals over 30 Hz. The frequencycomponent through the EEG telemeter 12 is recorded by a data recorder14. The EEG recording is passed through a band-pass filter 16 (8 to 13Hz) to extract α-wave components. Although both amplitude and frequencyfluctuations are observed in the extracted α-waves, focus is placed onfrequency fluctuation in the embodiment only because amplitude showssignificant differences among individuals. Of course, it is possible tofocus on amplitude fluctuations and analyze them based on the system andapparatus of the invention.

Among the frequency components having passed through the band passfilter 16, only those having an amplitude greater than a given level areconsidered as α-waves. Even when appearing to be α-waves, the filteredwaves are amplified as required, with reference to a level, in the casethat the subjects have only relatively limited EEG amplitude overall.

(ii) Extraction of Frequency Fluctuation in α-wave (Zero-CrossingMethod)

The datum line is set in the middle of the electric potentialfluctuations of the filtered wave, and pulse having a given potentialare generated each time the wave crosses the datum line in a givendirection (e.g. from negative to positive).

There are two methods for extracting the pulse train as fluctuation. Onemethod is to give a time constant to attenuation process of pulsepotential and accumulate potential for every pulse. This method isreferred to as method A. The other is to detect pulses successivelyusing computer, and to calculate a time interval (cycle) for everyconsecutive pulse. The reciprocal of the resulting value is convertedinto the time series of instant frequency (i.e. frequency is 1/cycle).This is referred to as method B. In method A, frequency fluctuation isdisplaced by analogue potential fluctuation. In method B, when arrangingthe calculated frequency for every wave in the sampling order (in theorder of elapsed time), frequency fluctuation in α-waves are extractedas a waveform consisting of points.

The forgoing processes are all computer-processible. However, theprocesses up to pulse generation and analogue output are preferablycarried out outside the computer.

(3) Analysis of Fluctuation Characteristics

Based on the extracted EEG fluctuation data, fluctuation characteristicsare analyzed.

(i) Histogram Method

This analysis is applicable to the data extracted by the above-mentionedmethod B. As preliminary processing, a specific frequency value in theα-wave frequency band is counted every 0.01 Hz to calculate frequencydistribution. Then, the mode value and frequency (or average frequency)corresponding to the mode value are calculated in order to extractdistribution characteristics.

(ii) Spectrum Method

This analysis is applicable to both method A and B. For the method A,the potential fluctuation is A/D converted by the computer at a givensampling frequency, and the digitalized data sequence is divided by aunit time. Based on the data in a unit time, power spectrum with respectto the fluctuation frequency is calculated via spectrum analysis by theFFT method.

For the method B, the time data recorded is divided into a number ofunit times, and data are re-sampled at a constant time period withineach unit time. Based on the unit data, a power level with respect tothe fluctuation frequency is calculated via spectrum analysis using theFFT method. These processes are carried out because of the fact thatspectrum analysis does not produce constant time intervals among plotsof changes in α-wave frequency converted into instant frequency, and toavoid a time lag between calculated and true sample lengths. Moreparticularly, instant frequency time series is produced from theobtained time data by the following processes.

Frequency Fm at a sampling period Sm is determined by the equation:

    Fm=1/{P.sub.n+1 -max(Pn)}

under the condition of:

    S.sub.m-1 <max(Pn)≦Sm≦P.sub.n+1

where the meaning of each of the letters is as follows.

Pn: generation time of the n-th pulse

S: sampling period

m: ordinal number

Sm: the m-th sampling period (determined by SXm)

Fm: the m-th sampled frequency

max(Pn): the maximum value of Pn till the sampling period

In this method, assuming that the sampling period is 50 ms (20 Hz),originally obtained time data are sampled without a sampling drop, andsample length (time interval) can be constant.

Then, from these time data, a tendency of changes in fluctuationspectrum with respect to fluctuation frequency is expressed in numericalvalues using the gradient of linear regression, so as to identify thecharacteristics of the changes. The fluctuation power value noticeablychanges after passing over a certain frequency. After identifying thatfrequency over which the gradient changes (i.e. inflecting frequency),the frequency band is separated into two band widths with the boundaryfrequency, that is, low and high frequency band widths, each of whichare regression-analyzed separately.

B-3. Psychological Evaluation Method for Alertness and Comfortableness

In psychology and psychophysiology, it is generally accepted that thepsychological approach is mainly based on two pivotal parameters,comfortableness and alertness, as representing the emotional conditionof individuals. It is preferable for the measurement of comfortablenessto set these parameters as a common and basic item and to selectadditional evaluation items depending on stimulations.

Psychological methods for evaluating comfortableness also include therating scale method, the semantic differential (SD) method, and analoguescale method, among which it is known that the analogue scale method isthe most suitable for evaluating feeling.

In evaluation of the psychological condition of the subjects with theaid of the evaluation table, it is preferable to make an assessmentbefore and after the physiological measurement, during both rest andexperimental conditions, to observe and review changes in psychologicalconditions as depicted by two sets of measurements.

B-4. Synthesis of the Result of Processing

Spectrum information calculated for each individual is related to thepsychologically evaluated values of comfortableness and alertness tofind correspondence between the values of fluctuation characteristicsand psychological conditions.

Although it is known that the frequency fluctuation characteristics ofthe α-waves are correlated to comfortableness and alertness, noeffective and accurate method has yet been established for determiningcorrespondence between these factors quantitatively.

The present invention uses NN (neural network) templates capable ofextracting characteristic components from multifaceted and non-lineardata, and classifying complicated information, to reveal an algorithmwhich can quantitatively estimate comfortableness and alertness withhigh precision. The following are preferred examples for embodying thisinvention.

C. PREPARATION OF NEURAL NETWORK TO ESTIMATE ALERTNESS ANDCOMFORTABLENESS

In the preferred embodiment, NN templates are prepared to estimatealertness and comfortableness from fluctuation in brain waves vialearning, based on data obtained from the physiological andpsychological experiments having been described above.

C-1. Experimental Data

In order to prepare NN templates for estimating alertness andcomfortableness, it is necessary to obtain experimental data used forthe learning of NN templates. FIG. 3 shows the construction of suchexperimental data used for training NN templates.

Data were obtained from the experimental system shown in FIG. 2, whichinclude brain waves of each subject (8 channels of F3, F4, C3, C4, P3,P4, 01, and 02) and corresponding psychological evaluation scores (as tocomfortableness and alertness). The values of 8 channels of brain wavesand the corresponding psychological scores are grouped into a set, andthe experimental data consisted of total of 1200 sets. These data werestatistically analyzed (for linear approximation). FIG. 10 presentscorrelations between the evaluation factors. Correlation betweenindividual fluctuation of brain waves for each channel for alertness andcomfortableness is indistinctive (although it is statisticallysignificant), which implies that it is difficult to estimate alertnessand comfortableness from brain waves using the conventional statisticalmethod.

C-2. NN template configuration

Configurations of NN for estimating alertness and comfortableness areshown in FIGS. 5A, 5B, 6A and 6B. The inventors found that alertness andcomfortableness are not independent from each other, but thecomfortableness is dependent on alertness (i.e. alertness affectscomfortableness). The NN template shown in FIG. 5A is suitable forestimating of alertness. Similarly, the NN template of FIG. 6A whichestimates comfortableness directly from fluctuation in brain waves andthe NN template of FIG. 6B which outputs alertness and comfortablenessat the same level are not sufficient for accurately estimatingcomfortableness. Instead, the NN template shown in FIG. 5B is much moreaccurate, which estimates comfortableness from both fluctuation in brainwaves and alertness.

In view of the above, the NN template for estimating comfortablenessbased on both α-wave fluctuation and alertness is constructed as acascade structure shown in FIG. 4 (NN template having composite outputof alertness and comfortableness). The input circuit layer of thealertness estimation template (NN_(alertness)) consists of 8 unitsrepresenting the α-wave fluctuation coefficients (8 channels of F3, F4,C3, C4, P3, P4, 01, and 02), while the output circuit layer consists ofa single unit representing alertness, as is shown in FIG. 5A.

On the other hand, the input circuit layer of the comfortablenessestimation template (NN_(comf)) consists of 9 units representing α-wavefluctuation coefficients (8 channels) and alertness, while the outputlayer consists of a single unit representing comfortableness (FIG. 5B).

D. SIMULATION EXPERIMENT AND RESULTS

The preparation of NN templates for estimating alertness (FIG. 5A) andcomfortableness (FIG. 5B) was simulated. The NN interior structure aftertraining, particularly the coupling strength between the input andoutput layers, was examined so as to observe the extent of the effect ofeach input on the output.

D-1. Experimental Result of Alertness Estimation NN

For the NN template for estimating alertness in FIG. 5A, fitting to 1100training data and 100 test data was simulated, varying the number ofhidden units (intermediate layers) and the number of training actions.First, the neural network was trained with learning data, then alertnesswas estimated from α-wave fluctuation using the trained NN template.Fitting to the training data and test data was observed, the results ofwhich are shown in FIGS. 7A, 7B, 8A and 8B. The experimental conditionsapplied were shown in FIG. 11.

The coupling strength between input and output layers in the respectcases was obtained to review the extent of the effect of input onoutput. The result is shown in FIG. 11 in the column of "dominantportion (where input significantly affects output)".

The extent of the effect was indicated with the correlation coefficientobtained from the coupling strength between each input (each channel ofbrain waves) and output (alertness). In other words, it is indicated asa value of coupling strength between each input and output (alertness)divided by total coupling strength.

D-2. Experimental Results of Comfortableness Estimation NN

For the NN template for estimating comfortableness in FIG. 5B, fittingto training data was preliminarily simulated in the same manner as thealertness estimation template. The result is shown in FIGS. 9A and 9B,and the experimental conditions, as well as the correlation betweeninput and output, is in FIG. 12.

In all simulations, the training rate coefficient, epsilon, was 0.01,the inertia term 0.9, and a three-layer sigmoid structure was used.

From the above-mentioned simulations, the following advantages areunderstood.

The optimum numbers of hidden units (intermediate layers) and trainingactions improve the accuracy, as well as fitting ability to test data,of the alertness estimation NN template, which realizes a practicalmethod for estimating psychological data.

The comfortableness estimation NN template is also improved byestimating comfortableness from both α-wave fluctuation and alertness,as well as by the optimum numbers of hidden units and training actions.

It is generally known (as an empirical law) that good results ofalertness measurement can be obtained from brain waves of the parietalregion of the brain, and that brain waves of the frontal region areeffective for measurement of comfortableness. The experimental resultsusing NN templates in accordance with the invention quantitativelyanalyzed and proved this theory.

E. HOURGLASS TYPE OF NEURAL NETWORK

In the above-described example, an algorithm is produced for estimatingpsychological parameters (alertness and comfortableness) from aphysiological parameter (EEG fluctuation), by using neural networks.

Training of the neural network is conducted by reversely propagatingerror signals from the output to the input side so as to minimize thesum of squares of differences between the network output and teachersignal (this procedure is called back propagation), thereby varying thesynaptic coupling weight between the first and second layers of thenetwork and between the second and third. The teacher signal isobtained, in this example, by an inquiry survey (questionnaire).

However, psychological evaluations used as teacher signals are based onan inquiry survey, and it generally contains a wide range of errors.This is due to dispersion of data caused by differences amongindividuals and experimental conditions. Thus, positively usingquestionnaire results as teacher signals involves problems.

Normally, the questionnaire method is used to measure alertness andcomfortableness during clinical psychological examination. However,correct results can be expected only when the subjects have thecapability of correctly understanding the meaning of the questions andcorrectly judging themselves when they answer honestly and without anypretension. It is very probable that psychological evaluation data (suchas alertness or comfortableness) contain inconsistencies. In addition,the psychological evaluation of alertness and comfortableness measuredby the questionnaire method has the disadvantage that the parameters arelimited to manifest characteristics recognizable in the subjectsconsciousness.

Comfortableness is mostly recognizable, and there is not so bigdifference between the actual comfortableness of the subject andpsychological evaluation obtained by a questionnaire. On the other hand,alertness or degree of fatigue is often non-recognizable, and it shouldbe expected that there is a relatively big difference between the actualcondition of the subject and evaluation based on the questionnaire.

In order to obviate such an adverse effect, it is preferable to use aneural network which is capable of learning, rather than usingpsychological evaluations as main parameters. One example of such aneural network is hourglass type of neural network.

The hourglass type of NN has been used in the field oftelecommunications for compression and decompression of information. Ithas also been applied to the study of human senses in recent years."Neural Network Model For Recognizing Shape Of a Grasped Object andDecides Hand Configuration" by Fukumura et al, Japan, IEICE, TechnicalReport, NC90-104, 1991-03, proposed an integrated model of differentkinds of information (visual sense and somatic sense) for motor controlof human arms. "Neural Network Model For Acquiring an InternalRepresentation Of the Weight Of Grasped Objects" by Uno et al. Trans.IEICE D-2, J76-D-2, 3, pp663-671, 1993-03, discloses a technique forestimating the weight of an unknown object to be gripped as an internalexpression in the middle layer of the neural network. For instance, whena man holds an object in his hand and moves his arm, a dynamics systemof the whole arm varies in accordance with the weight of the object, andtension of the arm muscle must be changed. But in reality, a man canappropriately move his arm in accordance with the weight of theobject,although he does not actually know the exact weight of theobject. This is considered to be because internal expression of theweight of the object has been obtained in the motor center throughexperience.

The above-mentioned publication of Uno et al. proposes a neural circuitmodel for obtaining internal expressions of the weight of the object tobe held, using observable data of articular (joint) angle representing aarm position and its driving torque. The basic idea of this technique isto construct a multi-layered neural network model by combining a networkfor calculating a weight of the object to be held, based on thearticular angle of the arm and its torque, with an inverse dynamicsnetwork for calculating a torque based on the weight of the object to beheld and the articular angle of the arm. This structure is shown in FIG.13. It is described in this publication that this structure enables thenetwork to learn the movement of the arm without positively (mainly)using the weight of the object to be held. After sufficient learning(training), the active value of the neurons in the intermediate layerbecomes a monotonic function of solely the weight of the object to beheld, without depending on the arm position. Namely, an internalexpression corresponding to the weight of the object has beenestablished in the neural network.

By supplying only a kinetic pattern and kinetic command as teachersignals to the neural network, the internal expression corresponding tothe weight is obtained as an activity value in the intermediate layer ofthe neural network. In order to indicate the weight as an internalexpression, it is preferable that the number of neurons in theintermediate layer is smaller than that in the other layers. This typeof network is a so-called hourglass type of neural network.

FIG. 14 shows a relationship between the weight of the object to be heldin the hand and the activity value of the neuron in the intermediatelayer (shown by the letter "X" in FIG. 13). The horizontal axisrepresents actual weight of the object held in the hand, which isunknown by the subject, and the vertical axis represents activity of theneuron X. The left graph plots activity values of the neuron withrespect to the actual load values obtained as a result of experiment,and the right graph shows internal expressions for non-learning data. Asis seen from the graph, the activity of the neuron X belonging to theintermediate layer is a monotonic function of the weight, and it isunderstood that an internal expression corresponding to the weight hasbeen established in the neural network.

When applying the hourglass type of neural network to the presentinvention, the network comprises a combination of a data compressionneural network for calculating a psychological evaluation value such asalertness and comfortableness from EEG fluctuation and a decompression(inverse) network for calculating EEG fluctuation from the psychologicalevaluation value, which constructs an hourglass type of multi-layeredneural network model having a small number of neurons in itsintermediate layer. In this structure, it is possible to obtain internalexpressions corresponding to alertness or comfortableness in the networkwithout directly using the psychological evaluation values for trainingof the network. In this case, the psychological evaluations areindirectly used to determined which neuron in the intermediate layer ofthe neural network after learning corresponds to alertness orcomfortableness. The hourglass type of neural network realizes accurateestimation of alertness and comfortableness from EEG fluctuation.

FIG. 15 shows a structural example of an hourglass type neural networkused in the invention for estimating alertness and comfortableness fromthe EEG fluctuation. The hourglass type neural network comprises athree-layered data compression NN and a decompression NN, which arecombined symmetrically. Inputs and outputs are units of physiologicalparameters (8 channels of EEG fluctuation coefficients) which are thesame as the EEG fluctuation signals used in the neural network shown inFIG. 5.

The training of this neural network is carried out by backwardlypropagating a difference signal between an output of the NN and ateacher signal (back propagation), from an output side to an input side,so as to minimize an addition of output of the NN and a square of thedifference between the teacher signal and the actual output, and byvarying the coupling load (weight) of synaptic coupling between thefirst and second layers, between second and third layers, between thirdand fourth layers, and between fourth and fifth layers. The feature ofthe present invention is that both the output signal and teacher signalused for training the neural network are 8 channels of EEG fluctuationcoefficients. By giving the EEG fluctuation coefficients to both theteacher signal and input signal for the learning of the neural network,neurons corresponding to the degree of alertness and comfortableness areformed in the intermediate layers. Thus, internal expression ofalertness and comfortableness are obtained in the third layer of theneural network.

The first and fifth layers of the neural network comprise 8 units(neurons) corresponding to 8 channels of EEG fluctuation coefficients.The second and fourth layers consist of 70 to 90 neurons. Logically, thethird layer must have at least 2 neurons to obtain internal expressionsof alertness and comfortableness, but it actually needs more neurons.The number of neurons in the third layer is set so as to allow thepsychological evaluation to appear as a constant pattern. This actuallydepend on the EEG fluctuation coefficient data used for training theneural network, and an appropriate number of neurons should be selectedthrough experiment action.

The obtained internal expressions can be confirmed by comparing eachoutput of the third layer, which has been obtained by inputting the EEGfluctuation, with the psychological evaluation value (degree ofalertness and comfortableness), which has been obtained from thequestionnaire. Thus, the psychological evaluation values such asalertness or comfortableness obtained from the questionnaire are notdirectly used for training the neural network, but are used forreviewing which internal expression corresponds to which psychologicalparameter. The internal expression of the psychological condition may beobtained as a single output value of the third layer of the neuralnetwork (shown in FIG. 15) for some cases, or alternatively it may beobtained as a constant output pattern of the whole units for othercases. The publication by Fukumura et al. mentioned above shows that theactivity pattern of the neurons in the intermediate layer variesdepending on the shape of the object to be held, for example, acylindrical, cubic, or spherical shape.

The graph in FIG. 16A shows a correlation between the output values ofthe first unit of the third layer and the alertness obtained from thequestionnaire, while the graph in FIG. 16B shows a correlation betweenthe output values of the second unit of the third layer and thecomfortableness obtained from the questionnaire. The horizontal axisrepresents psychological evaluation obtained from the questionnaire, andthe vertical axis represents actual output value of the third layer. Inthis example, the first unit of the third layer is used for outputtingdegree of alertness and the second unit is used for outputting degree ofcomfortableness.

In these graphs, the output of a certain unit of the third layer isobtained as a result of inputting various patterns of the EEGfluctuation coefficients into the trained hourglass type neural network.As can be seen from the graphs, the output of the first and second unitsof the third layer have a highly correlated relation with thequestionnaire result of alertness and comfortableness, respectively. Inother words, the internal expressions corresponding to alertness andcomfortableness are obtained in the first and second units,respectively.

Since the training of the neural network is carried out using only aphysiological parameter (EEG fluctuation signal), the degree ofalertness or comfortableness obtained in each unit of the third layerdoes not contain the variation (dispersion) in psychological evaluationfrom the questionnaire. In this regard, the hourglass type neuralnetwork is capable of more accurate estimation compared with the simplethree-layered neural network described in the above subsections A-E.

In FIG. 16, it seems that the estimation values of alertness andcomfortableness obtained by the hourglass type neural network are notconsistent with the questionnaire evaluations and that they indicatevariation. However, this variation is caused by the problems of thequestionnaire method.

The simple three-layered neural network directly utilizes psychologicalevaluation values as teacher signals for training the neural network.The resultant psychological conditions estimated by such a neuralnetwork are limited to recognizable psychological conditions (such ascomfortableness) of which the subject can be conscious. On the otherhand, the hourglass type neural network does not directly utilize thepsychological evaluations as teacher signals, and is capable ofestimating such psychological conditions that are difficult for thesubject to recognize (alertness or degree of fatigue).

Although it has been described in the above-mentioned examples thatpsychological evaluations obtained by the questionnaire are used asparameters of alertness, work results of selective reaction tests may beused as parameters instead of the psychological evaluation. In thiscase, the EEG fluctuation coefficients during the selective reactiontest and the work results are measured, and the neural network istrained based on these data. Alertness and the degree of fatigue areestimated from the EEG fluctuation during actual working, by the thustrained neural network.

It is known that the work results of the selective reaction testsreflect the degrees of alertness and comfortableness rather than thepsychological evaluations. However, it is difficult to simultaneouslycarry out such test during the actual working. For example, it is almostimpossible to perform selective reaction testing during the actualdriving of the car. For this reason, psychological evaluations, whichare measurable during actual working, have been used for real timemeasurement of the degree of alertness or fatigue, instead of thereal-time work results.

In the present invention, the work result, which is difficult to correctduring the actual working, is substituted by the EEG fluctuation as aphysical parameter. This may achieve the same accuracy of real-timeestimation of alertness or degree of fatigue as using work results. Bymaking the neural network previously learn the relation between the workresult and the EEG fluctuation, good estimation of alertness or degreeof fatigue can be obtained by such a neural network.

FIG. 17 shows this method, that is, making the neural network learn therelation between the EEG fluctuation and work result and estimatingalertness or degree of fatigue using the trained neural network. In theconventional method, psychological evaluations are obtained from thequestionnaire during the actual driving because it is difficult to carryout selective reaction test simultaneously with driving action. Thispsychological evaluation and the corresponding EEG fluctuation are usedas preliminary test data for learning of the environment. Then,alertness or degree of fatigue is estimated from the EEG fluctuationduring the actual driving. On the contrary, in the present invention,the neural network previously learns the relation between the EEGfluctuation obtained during the experiment (e.g. selective reactiontest) and alertness or degree of fatigue, using work results, and thenestimates alertness or degree of fatigue during the actual driving.

By using working results which are considered to be more closelyassociated with alertness, rather than psychological evaluation usingthe questionnaire, the accurate analysis of information relating tophysical and psychological conditions can be achieved by the vitalinformation analyzing apparatus of the present invention.

For obtaining working results, Uchida-Kraepelin's test can be used, aswell as selective reaction tests, and various known tests can beapplicable to the present invention.

As a conclusion, the neural network used in this invention can estimatepsychological conditions including alertness and comfortableness basedon the input EEG fluctuation signals.

When combining two neural networks for estimating alertness andcomfortableness, respectively, more accurate estimation can be achievedbecause comfortableness is estimated taking the first estimatedalertness into consideration.

When using an hourglass type neural network, the training of the neuralnetwork is carried out using the EEG fluctuation signals and internalexpressions corresponding psychological conditions can be obtained inthe intermediate layer of the neural network without directly using thequestionnaire evaluation.

Those skilled in the art can make many substitutions or modifications ofthe embodiments described above, without departing from the scope andspirit of the appended claims.

What is claimed is:
 1. An apparatus for analyzing a physiologicalfluctuation signal of a subject to determine at least one psychologicalcondition of the subject, the apparatus comprising a neural networkreceiving the physiological fluctuation signal as an input forestimating physiological conditions using frequency variations, whereinsaid neural network is an hourglass type neural network, training of thehourglass type neural network carried out by supplying the physiologicalfluctuation signal to both an input and an output of the hourglass typeneural network, output values of an intermediate layer of the hourglasstype neural network representing at least one psychological condition.2. The apparatus according to claim 1, wherein said neural networkreceives a pre-processed EEG fluctuation signal as a physiologicalfluctuation signal.
 3. The apparatus of claim 2, wherein saidhourglass-type neural network outputs a signal indicative of analertness of the subject as the at least one psychological condition ofthe subject.
 4. The apparatus of claim 2, wherein said hourglass typeneural network outputs a signal indicative of a comfortableness of thesubject as the at least one psychological condition of the subject. 5.The apparatus of claim 1, further comprising signal sensing means,attachable to the subject, for sensing a fluctuating physiologicalcondition of the subject and outputting the physiological fluctuationsignal.
 6. The apparatus of claim 1, wherein the physiologicalfluctuation signal is an EEG fluctuation signal.
 7. An apparatus foranalyzing information relating to physiological and psychologicalconditions comprising a neural network receiving a preprocessed EEGfluctuation signal of a subject as an input for estimating physiologicalconditions of the subject, wherein said neural network comprises:a firstneural network receiving the pre-processed EEG fluctuation signal as aninput for estimating a degree of alertness; and a second neural networkreceiving the degree of alertness estimated by the first neural networkand the pre-processed EEG fluctuation signal as inputs for estimatingcomfortableness, to estimate both alertness and comfortableness aspsychological conditions.
 8. The apparatus according to claim 7, whereinsaid first and second neural networks are hourglass type neuralnetworks, the EEG fluctuation signals are supplied to both input andoutput of each of the neural networks for training the neural networks,and output of an intermediate layers of the neural network representsthe psychological conditions.
 9. The apparatus of claim 5, furthercomprising:signal sensing means, attachable to the subject for sensingan EEG fluctuation signal; and processing means for generating thepreprocessed EEG fluctuation signal from the EEG fluctuation signal. 10.A method for analyzing information relating physiological andpsychological conditions, comprising:applying a physiologicalfluctuation signal to a neural network; and estimating psychologicalconditions using frequency variations; wherein said neural network is anhourglass type neural network, training of the hourglass type neuralnetwork carried out by supplying the physiological fluctuation signal toboth an input and an output of the hourglass type neural network, outputvalues of an intermediate layer of the hourglass type neural networkrepresenting the psychological conditions.
 11. The method according toclaim 10 wherein said physiological fluctuation signal includes apre-processed EEG fluctuation signal.
 12. The method according to claim11, wherein said psychological conditions include alertness.
 13. Themethod according to claim 11, wherein said psychological conditionsinclude comfortableness.
 14. The method of claim 6, wherein thephysiological fluctuation signal is an EEG fluctuation signal.
 15. Amethod for analyzing information relating physiological andpsychological conditions, comprising:applying a physiologicalfluctuation signal of a subject to a neural network, the physiologicalfluctuation signal including a pre-processed EEG fluctuation signal ofthe subject; applying the pre-processed EEG fluctuation signal to analertness estimation portion of the neural network to estimatealertness; and applying the estimated alertness and the pre-processedEEG fluctuation signal to a comfortableness estimation portion of theneural network to estimate both alertness and comfortableness as thepsychological conditions.
 16. The method according to claim 15, whereinthe alertness estimation neural network and the comfortablenessestimation neural network are hourglass type neural networks, both ofwhich have been trained with the EEG fluctuation signals at both inputand output, and the output of an intermediate layer of each neuralnetwork represents the psychological conditions.